Porting for torque
I'm totally with you on the exhaust ports, but how can you open the intake port earlier and not have greater overlap? And then the overlap causes dilution under off-boost conditions (spool up). Whereas later intake closing will hurt low end, but in a different way because it doesn't affect overlap in the same way.
It'd be nice to have some 1D modeling or an engine dyno...
Yes, you would have more overlap with the intake opening earlier.
But, I maintain its the "right kind" of overlap and in about the right proportion.
With the stock opening at 32 or 45 degrees After Bottom Dead Center your expanding intake chamber is "sucking" exhaust into the intake stroke for 32 or 45 degrees before the intake port opens and allows it to start "sucking" intake air/fuel in. Even with an early opening street port you are at around 24deg ABDC. You have to reposition the side seals, put in a larger corner seal and bevel the rotor edge to even get to 0deg ABDC (like RX-8).
Getting the intake port open a little earlier will stop you from sucking in as much exhaust for both less dilution and lessening of the reversion wave when the intake port does open and gets the intake open while the exhaust velocity is a bit higher for more intake scavenging kick starting the inertia needed for good intake chamber filling.
If you port the exhaust up and leave the intake port at stock opening you now have less velocity at the exhaust port when the intake opens since it is further from the blow down phase. This means you have less scavenging from the exhaust to pull the intake mixture through and kick start the intake inertia for good intake chamber filling.
Physical size difference from porting the exhaust port up also means less velocity for less scavenging of intake and exhaust.
I would be very interested to see how a bridge or semi peripheral ported renesis responds with a turbo.
I think you are thinking of exhaust pushing its way into the intake during overlap. This isn't the case, you are losing intake to the exhaust port.
If you eliminate the EGR valve, crankcase ventilation and evaporative emissions from a rotary your intake ports and intake manifold remain clean and carbon free. How is this possible if all that exhaust is pushing up into the intake chamber when the throttle plates are closed?
If you take apart a peripheral port or bridge port race motor is the intake carboned up? Yet there is enough exhaust dilution that the motor misfires constantly at idle.
Its because the closed throttle plate prevents the intake stroke from pulling in enough air to both feed the loss to the exhaust port and fill the expanding intake chamber during overlap so it overcomes the vacuum from the exhaust scavenging the intake chamber and sucks exhaust in. The exhaust is being sucked by the expanding rotor/rotor chamber which is swept clean by the seals. There is no draw from the intake ports so they remain clean.
It'd be nice to have some 1D modeling or an engine dyno...
Yes, you would have more overlap with the intake opening earlier.
But, I maintain its the "right kind" of overlap and in about the right proportion.
With the stock opening at 32 or 45 degrees After Bottom Dead Center your expanding intake chamber is "sucking" exhaust into the intake stroke for 32 or 45 degrees before the intake port opens and allows it to start "sucking" intake air/fuel in. Even with an early opening street port you are at around 24deg ABDC. You have to reposition the side seals, put in a larger corner seal and bevel the rotor edge to even get to 0deg ABDC (like RX-8).
Getting the intake port open a little earlier will stop you from sucking in as much exhaust for both less dilution and lessening of the reversion wave when the intake port does open and gets the intake open while the exhaust velocity is a bit higher for more intake scavenging kick starting the inertia needed for good intake chamber filling.
If you port the exhaust up and leave the intake port at stock opening you now have less velocity at the exhaust port when the intake opens since it is further from the blow down phase. This means you have less scavenging from the exhaust to pull the intake mixture through and kick start the intake inertia for good intake chamber filling.
Physical size difference from porting the exhaust port up also means less velocity for less scavenging of intake and exhaust.
I would be very interested to see how a bridge or semi peripheral ported renesis responds with a turbo.
I think you are thinking of exhaust pushing its way into the intake during overlap. This isn't the case, you are losing intake to the exhaust port.
If you eliminate the EGR valve, crankcase ventilation and evaporative emissions from a rotary your intake ports and intake manifold remain clean and carbon free. How is this possible if all that exhaust is pushing up into the intake chamber when the throttle plates are closed?
If you take apart a peripheral port or bridge port race motor is the intake carboned up? Yet there is enough exhaust dilution that the motor misfires constantly at idle.
Its because the closed throttle plate prevents the intake stroke from pulling in enough air to both feed the loss to the exhaust port and fill the expanding intake chamber during overlap so it overcomes the vacuum from the exhaust scavenging the intake chamber and sucks exhaust in. The exhaust is being sucked by the expanding rotor/rotor chamber which is swept clean by the seals. There is no draw from the intake ports so they remain clean.
Engine Port Test #1
Massive Exhaust port (earlier open and later close than 13BREW)
Street Port with no early open, late close (32ATDC open on all runners, 60-70ABDC closing on primary ports, 50-60ABDC closing on secondary ports)
Engine Port Test #2
Same Massive Exhaust port (earlier open and later close than 13BREW)
Massive Street port intake taken to full wide limit, any more and side seal would fall in. Intake port taken to larger height than previously. (~15ABDC on all runners, ~65-75 ABDC on all runners)
Engine #1 Would idle at 850-900rpm with reasonable vacuum
Engine #2 Would idle at 1150rpm with poor vacuum
I went from 32ATDC open to ~15ATDC open and I needed 200rpm extra to keep it idling at a poorer vacuum. Stank of fuel, used a lot more fuel. Certainly had less power at lower throttle openings.
I do not agree that carbon stains or not in the intake manifold do or do not mean that there is intake manifold exhaust gas contamination. The only action for my new found 'poor idling' engine was the vacuum in the intake manifold is being filled with partially combusted exhaust gas.
Be reasonable for a second. At a base atmosphere at sea level there will be 101.3kPA ambient. There will always be at least 110kPA at a guess in your exhaust manifold even idling. When your engine is ticking over at idle there will always be 40-60kPA ABSOLUTE ie -40 to -60kPA in the intake manifold. Gas is going to rush past the rotor trench and fill the entire volume below the throttle blade during that overlap period every time the engine goes around. To say anything else is delusional.
well, i'm sure he can answer, retort, whatever ... for himself, so this is not me speaking for him. however, in both of your cases/examples, you've exacerbated the dilution by changing the exhaust closing edge and i'm pretty sure that while his assertions are pro early intake opening, he explicitly deterred getting overlap through exhaust porting.
that said, there is no huge surprise in what you found with your two test engines. it is pretty much what I would expect.
that said, there is no huge surprise in what you found with your two test engines. it is pretty much what I would expect.
well, i'm sure he can answer, retort, whatever ... for himself, so this is not me speaking for him. however, in both of your cases/examples, you've exacerbated the dilution by changing the exhaust closing edge and i'm pretty sure that while his assertions are pro early intake opening, he explicitly deterred getting overlap through exhaust porting.
that said, there is no huge surprise in what you found with your two test engines. it is pretty much what I would expect.
that said, there is no huge surprise in what you found with your two test engines. it is pretty much what I would expect.
I will say that the first test engine returned good fuel economy when non turbo. It used less fuel non turbo than the worn out stock port engine it replaced. And yes it too had noticeably less power below 4000rpm than the original worn out stock port engine.
Other thing to note is that that engine setup had excellent flow. It made more power than I originally thought possible on 1 bar boost.
Test engine 2 did not last long enough to get any results about power, but it felt very strong once you were above the point where the ports started working right.
I can not agree with your conclusions that early opening ports do not cause extra change dilution. If fact I strongly disagree. I have back to back built an engine of the following parameters.
Engine Port Test #1
Massive Exhaust port (earlier open and later close than 13BREW)
Street Port with no early open, late close (32ATDC open on all runners, 60-70ABDC closing on primary ports, 50-60ABDC closing on secondary ports)
Engine Port Test #2
Same Massive Exhaust port (earlier open and later close than 13BREW)
Massive Street port intake taken to full wide limit, any more and side seal would fall in. Intake port taken to larger height than previously. (~15ABDC on all runners, ~65-75 ABDC on all runners)
Engine #1 Would idle at 850-900rpm with reasonable vacuum
Engine #2 Would idle at 1150rpm with poor vacuum
I went from 32ATDC open to ~15ATDC open and I needed 200rpm extra to keep it idling at a poorer vacuum. Stank of fuel, used a lot more fuel. Certainly had less power at lower throttle openings.
I do not agree that carbon stains or not in the intake manifold do or do not mean that there is intake manifold exhaust gas contamination. The only action for my new found 'poor idling' engine was the vacuum in the intake manifold is being filled with partially combusted exhaust gas.
Be reasonable for a second. At a base atmosphere at sea level there will be 101.3kPA ambient. There will always be at least 110kPA at a guess in your exhaust manifold even idling. When your engine is ticking over at idle there will always be 40-60kPA ABSOLUTE ie -40 to -60kPA in the intake manifold. Gas is going to rush past the rotor trench and fill the entire volume below the throttle blade during that overlap period every time the engine goes around. To say anything else is delusional.
__________________
I agree with everything you have written and I don't believe it contradicts anything I have written.
I stated there is exhaust dilution from overlap at low load (throttle plates closed). The vacuum created by the expanding intake stroke combined with flow being limited by closed throttle plates has to reverse the normal overlap dynamic and suck exhaust into the intake stroke instead of air.
The normal dynamic is intake loss out the exhaust from the venturi created by high velocity exhaust gas exiting the exhaust port.
You are describing driveability problems and not power output. Power output is measured at full throttle.
As I showed with the charts comparing peripheral port intake to sideport intake the high overlap motor makes more power at all rpms.
Yes, you can make a high overlap motor that makes less power than a low overlap motor- but the charts are comparing optimized engines being evaluated for production vehicles.
There isn't some magical rpm where the exhaust port starts scavenging the intake charge, but rather it is the normal dynamic that the closed throttle plate interferes with.
Mazda and Curtis-Wright (OMP) chose side port intake for production.
Mazda, NSU, Suzuki, Norton, Citroen, Mercedes and others I can't think of chose peripheral intake ports.
There were some ingenious ways of dealing with the driveability from low load high overlap exhaust reversion.
NSU used a torque converter on its manual transmission peripheral port RO-80 to dampen the torque fluxuations at part throttle. They chose to let it brap, but drive smoothly.
Norton idled on one rotor of its two rotor peripheral port engine leaving the other rotor as drag on the idling rotor to increase load (open throttle more). Smooth idle at 850rpm from decreased charge dilution.
Engine Port Test #1
Massive Exhaust port (earlier open and later close than 13BREW)
Street Port with no early open, late close (32ATDC open on all runners, 60-70ABDC closing on primary ports, 50-60ABDC closing on secondary ports)
Engine Port Test #2
Same Massive Exhaust port (earlier open and later close than 13BREW)
Massive Street port intake taken to full wide limit, any more and side seal would fall in. Intake port taken to larger height than previously. (~15ABDC on all runners, ~65-75 ABDC on all runners)
Engine #1 Would idle at 850-900rpm with reasonable vacuum
Engine #2 Would idle at 1150rpm with poor vacuum
I went from 32ATDC open to ~15ATDC open and I needed 200rpm extra to keep it idling at a poorer vacuum. Stank of fuel, used a lot more fuel. Certainly had less power at lower throttle openings.
I do not agree that carbon stains or not in the intake manifold do or do not mean that there is intake manifold exhaust gas contamination. The only action for my new found 'poor idling' engine was the vacuum in the intake manifold is being filled with partially combusted exhaust gas.
Be reasonable for a second. At a base atmosphere at sea level there will be 101.3kPA ambient. There will always be at least 110kPA at a guess in your exhaust manifold even idling. When your engine is ticking over at idle there will always be 40-60kPA ABSOLUTE ie -40 to -60kPA in the intake manifold. Gas is going to rush past the rotor trench and fill the entire volume below the throttle blade during that overlap period every time the engine goes around. To say anything else is delusional.
__________________
I agree with everything you have written and I don't believe it contradicts anything I have written.
I stated there is exhaust dilution from overlap at low load (throttle plates closed). The vacuum created by the expanding intake stroke combined with flow being limited by closed throttle plates has to reverse the normal overlap dynamic and suck exhaust into the intake stroke instead of air.
The normal dynamic is intake loss out the exhaust from the venturi created by high velocity exhaust gas exiting the exhaust port.
You are describing driveability problems and not power output. Power output is measured at full throttle.
As I showed with the charts comparing peripheral port intake to sideport intake the high overlap motor makes more power at all rpms.
Yes, you can make a high overlap motor that makes less power than a low overlap motor- but the charts are comparing optimized engines being evaluated for production vehicles.
There isn't some magical rpm where the exhaust port starts scavenging the intake charge, but rather it is the normal dynamic that the closed throttle plate interferes with.
Mazda and Curtis-Wright (OMP) chose side port intake for production.
Mazda, NSU, Suzuki, Norton, Citroen, Mercedes and others I can't think of chose peripheral intake ports.
There were some ingenious ways of dealing with the driveability from low load high overlap exhaust reversion.
NSU used a torque converter on its manual transmission peripheral port RO-80 to dampen the torque fluxuations at part throttle. They chose to let it brap, but drive smoothly.
Norton idled on one rotor of its two rotor peripheral port engine leaving the other rotor as drag on the idling rotor to increase load (open throttle more). Smooth idle at 850rpm from decreased charge dilution.
Thread
Thread Starter
Forum
Replies
Last Post
HalifaxFD
Canadian Forum
126
May 9, 2016 07:06 PM
